Oracle Database Discussions

When I try to run the following command:

drop sequence mst_scenario_attribute_wbs_SQ;

I get the following error:

ORA-02289: sequence does not exist

I know it exists because I see it when I query:

select *
from sys.all_sequences s

I also see it in PL/SQL Developer

I tried to purge the recycle bin, but that didn't do anything. Also, the DB has been restarted. Any ideas?